For clarity of communication the following discussion will refer to, peroxygen compounds but it will be understood that this term implies the use of either hydrogen peroxide, other peroxygen molecules, such as peracetic acid and longer chain peroxycarboxylic acids, other organic peroxides such as urea peroxide, and other organic and inorganic pre-curser chemicals for the in-situ creation of hydrogen peroxide such as sodium peroxide, benzyl peroxide and the like.
The universal reliance on techniques such as refrigeration, drying and the addition of preservative chemicals to foods highlights the need for effective and efficient methods to extend the length of time that foodstuffs can be stored safely and without risk to human consumption.
Ideally, it would be useful if a device and/or process could be found which utilized a readily available, naturally occurring, relatively non-toxic, non-aromatic and inexpensive chemical which would aid in the preservation of foods and extend their shelf life under normal storage conditions such as those found in refrigerators, cool rooms, freezers and other air conditioned spaces. It would also be ideal if the device/process of choice eliminated malodors and allowed the natural aromas of the foods to predominate. In addition it would also be advantageous for occupational health and safety reasons if the chemical and device used provided an environment, which is safe to work in without the need for additional safety equipment. Peroxygen compounds, appear to fit these requirements.
Peroxygen compounds have a well, accepted history of being excellent disinfectant and sterilization agents. In particular Ernest Barbieri (Swiss patent 715,765) teaches us that the conditioning of air in a sealed chamber containing fresh fruit and vegetables will extend their shelf life. Such conditioning entails the removal of ethylene oxide from the chamber, the disinfection of the air in the chamber by hydrogen peroxide and the control of temperature at a level appropriate for the food being preserved, unfortunately he does not disclose the temperatures of concern nor the concentration of hydrogen peroxide required for the treatment. See also, for example US Pat No US2004022907, which discloses the use of high concentrations of hydrogen peroxide vapor over a short period of time 15-30 seconds to treat Almonds, other nuts, grains, dried or dehydrated fruits or vegetables, and other agricultural foodstuffs moving along a conveyor. This treatment could be performed with peroxide vapor concentrations ranging from 0.1 to 10 mg/L of treatment air, at temperatures below 40 deg. C. Further, techniques for the preservation of foods, which have been reported, include the use of vaporous or liquid peroxides either directly as hydrogen peroxide or indirectly as organic or inorganic peroxy compounds see for example U.S. Pat. Nos. 5,200,189, 5,314,687, 5,409,713, 5,437,868, 5,489,434, 6,674,538, 6,010,729, 6,111,963, and 6,514,556). These techniques are usually applied at temperatures of 20 deg. C.-80 deg. C. prior to the objects being stored in an air-conditioned, refrigerated or other suitable space, or transported for further processing or preservation.
It is well demonstrated in the art described above and elsewhere that the higher the temperature the greater the biocidal activity of peroxygen compounds in both liquid and vapor forms, and it has also been hitherto believed that at sufficiently low concentrations and temperatures the efficacy of peroxygen compounds is reduced to a level which is ineffective.
Some prior art exists for the chemical treatment of fresh produce at refrigeration temperatures, for example U.S. Pat. No. 6,666,030 ‘Ice Composition containing hydrogen peroxide and method for storing perishable foods’, teaches how the very low vapor pressure of hydrogen peroxide ensures it remains in the ice for a longer period of time than more volatile oxidative chemicals such as ozone. This allows the peroxide/ice composition created by electrolytic means to be used for the effective storage of fresh fish, fruit and vegetables at or near 0° C. For this prior art to be effective it requires an ice composition of 50-500 mg/L of hydrogen peroxide to be in constant contact with the foods being preserved.
U.S. Pat. No. 5,460,845 ‘Peroxyacid Antimicrobial composition’ teaches that particular synergistic combinations of peroxyacids form effective sanitizing solutions for the sanitizing of food processing equipment and clothing in the temperature range of 4-60° C. and in use liquid concentrations of peroxyacids in excess of 30 ppm. It also requires that the liquid formulations thus described make direct contact with the surfaces or products to be sanitized.
US Patent Application 2005/0089458 ‘Refrigeration Purifier’ teaches the use of ozone produced by corona discharge dissolved in the water used in refrigeration systems, with offgasing of un-dissolved ozone within the refrigerated space decontaminating the air and non-wetted surfaces. The method of liquid decontamination is via the dissolution of ozone and subsequent formation of hydroxyl radicals and hydrogen peroxide produced by the reaction of ozone with water. Some difficulties associated with the use of ozone in this manner are the potential corrosion and occupational health and safety issues of high levels of ozone in cool rooms and the like.
US Patent Application 2004/0151812 ‘Method for Preserving Fresh Vegetables’ discloses a method for packaging fresh foods under a controlled atmosphere containing initially high levels of carbon dioxide (or other anti-microbial gas or vapors), and subsequently allowing the level of carbon dioxide to fall below 20% of the atmosphere in the packaging by use of semi-permeable membranes and the like over a period of 1-7 days. The use of peroxide is mentioned in this document, but its method of application is not specified or described and as required by their claims, the generation vapor levels of peroxide equivalent to or greater than 20% of the atmosphere would pose a significant occupational health and safety hazard and potentially damage any produce stored under these conditions.
European Patent 1043273 ‘Hydrogen Peroxide Solution, Method of Using Said Hydrogen Peroxide Solution, and Method for Producing Said Hydrogen Peroxide Solution, teaches about a means for stabilizing high concentrations of hydrogen peroxide by the addition of polyalcohols and organic acids to the formulation. It also discloses a multitude of uses such as the disinfection of products or spaces by the direct application of an atomized solution onto the product or into the space to be disinfected. It also teaches that a significant amount of hydrogen peroxide is added to the product (0.1-1 g hydrogen peroxide per kg of product). At these levels the proposed use of treating the cooling air in bakeries and slaughterhouses would result in significant workplace hazards. The recommended safe limit (TLV-TWA 8 hours) in the workplace of hydrogen peroxide vapors is 1.4 mg/kg Air (1 ppm)
We disclose herein a device and method, which utilizes the advantages of refrigeration in a synergistic manner with the advantages of peroxygen compounds, with respect to their ability to reduce and/or eliminate microbial activity and mitigate malodors within the treated space. This device and method can use a chemical which is—naturally occurring and applies it at vapor levels significantly lower than previously thought useful, at such low vapor levels where the process is non hazardous to operators in the food handling and processing industries. The underlying basis of this invention is the drive towards equilibrium of peroxide vapor above a reservoir of bulk peroxygen compound. This drive produces a continuous supply of peroxygen compounds in the vapor state to react with microorganisms and malodorous chemicals within the treatment space, such organisms and chemicals remove the peroxygen compounds from the vapor state thereby allowing the release of further peroxygen vapors from the reservoir of the bulk solution. When the peroxygen compound is hydrogen peroxide, it has one additional advantage in that it spontaneously decomposes to water and oxygen in the vapor state in accordance with the following equation (1)2H2O2(l)<<2H2O(g)+O2  (1)
Although this patent describes particular application of the process to the preservation of fresh food and vegetables, it would be appreciated, by anyone skilled in the art, that the techniques described herein are applicable to any enclosed or semi-enclosed space within which objects, which require a bacterial, mould and/or malodor free environment can be stored.